1. Field of the Invention
The invention relates to a pneumatic vehicle tire comprising a one- or two-ply carcass, which extends between two bead rings having associated bead apexes, a belt arrangement provided between the carcass and a tread strip, and also rubber reinforcing plies arranged in the sidewall regions, which adopt a supporting function when the tire is deflated.
2. Prior Art
Pneumatic vehicle tires of this kind are, for example, known from U.S. Pat. No. 5,368,082. It is possible, by means of such tires, in the event of a puncture, to allow travel with a deflated tire over larger distances at adequate speed before a repair of the tire or a change of the tire has to be effected. Such tires accordingly increase safety in the event of a puncture and make it possible to reach the next repair workshop without problem, so that undesired tire changing can be avoided which is also dangerous on roads with heavy traffic.
The object of the present invention is to so design a pneumatic vehicle tire of the initially named kind that a high mileage is possible at an adequately high speed, even in the deflated state, with the stiffening rubber plies provided in the sidewalls not disturbingly impairing the riding comfort of the tire when operated at normal pressure and with the weight of the tire remaining as small as possible.
This object is satisfied in accordance with the invention essentially in that a rubber reinforcing ply is arranged in the sidewall regions radially within a first carcass ply and its maximum thickness is disposed in the upper half of the sidewall height; in that the rubber reinforcing ply extends, starting from the bead apex region, up to and beneath the edge region of the belt ply, and in that the bead apex, which extends approximately up to the half sidewall height, is surrounded by the first carcass ply, which is led around the respective bead core.
The rubber reinforcing ply and the bead apex preferably consist of the same rubber mixture.
As a result of the choice of the rubber mixture, of the thickness of the rubber reinforcing ply and of the cure times of this rubber reinforcing ply, which respectively differ in dependence on the position of the rubber reinforcing ply in the tire, ideal values are obtained with regard to the long running characteristics when the tire is deflated, in particular when, as a result of the mixtures that are used and of the selective hardening time in the finished tire, the modulus of elasticity E* of the rubber reinforcing plies and also of the bead apex is the same as or greater than 9 Mpa and the tan xcex4 value is the same as or smaller than 0.03 (measured by means of xe2x80x9cEPLEXORxe2x80x9d, 10 Hz, 10% prestress and 1% DSA). The hardness IRHD of this rubber reinforcing ply and also of the bead apex is preferably the same as or greater than 80 when measured at room temperature. The measurement of the IRHD (International Rubber Hardness Degree) takes place analogously to the Shore hardness measurement, but with a ball-shaped measuring tip. The measurement or testing takes place in this connection in accordance with DIN 53519, with the so-called microhardness being determined, since small samples are measured which are taken from the respective tire.
The rubber reinforcing ply and the bead apex are preferably manufactured from a rubber mixture which is a polymer mixture of natural rubber (NR)/isoprene rubber (IR) and butadiene rubber (BR), with at least 50 parts NR/IR being contained in this polymer mixture, a carbon black content of 50 to 60 parts, preferably of a rapidly injectable FEF carbon black, and also 5 to 8 parts zinc oxide, 2 parts stearic acid, 1.5 parts aging protection agent, and also one or more parts vulcanization accelerator and sulfur (preferably 4 to 5 parts), in order to keep the loss characteristics of the mixture low.
In the event of using an additional second carcass ply, the basic construction of the tire with a single layer carcass is retained largely unchanged. The second carcass ply being provided radially outside the first carcass ply and extending up to and into the upper third of the height of the sidewall while lying against the first carcass ply and preferably terminating in the bead side bead apex region, while lying against the end region of the first carcass ply turned around the bead core. In this arrangement the turned over end of the first carcass ply is in particular led upwardly into the top third of the sidewall height between the two carcass plies and is directly connected to them. In this way the advantage is achieved, in comparison to tires with two ply carcasses and a reinforcing ply also provided in the sidewall region between the two carcass plies, that both carcass plies are only exposed to a small compression in the upper third of the sidewall region, which is in particular of special significance when carcass plies of Kevlar are used, which shouldxe2x80x94as far as possiblexe2x80x94not be exposed to any form of compression.
In the regions of the sidewall in which the two carcass plies extend lying against one another, it is advantageous to introduce an elastic buffer layer between the two carcass plies in order to achieve a certain relative mobility between the two plies and a defined stiffness as a result of the spacing that is set.
Further advantageous embodiments of the invention are set forth in the subordinate claims.